1. Field of the Invention
This invention relates to an improved method for simultaneously resin-packaging electronic components on a pair of leadframes. The present invention also relates to an improved mold used in such a method.
2. Description of the Prior Art
Generally, electronic components such as IC's and transistors are produced by using leadframes. Specifically, semiconductor chips are first mounted on the leadframe at constant spacing, and subsequently packaged in synthetic resin. After hardening of the resin, the packaged electronic components are separated from the leadframe.
Conventionally, the so-called multi-molding technique has been often adopted for resin-packaging electronic. components simultaneously with respect to a pair of leadframes. According to such a technique, use is made of a specific mold such as shown in FIGS. 4 and 5.
Specifically, as shown in FIGS. 4 and 5, the prior art mold, which is generally designated by reference numeral 10, consists of a lower mold member 20 and a upper mold member 30. The upper and lower mold members together form two rows of molding cavities C1O, C20. The two cavity rows are spaced transversely from but arranged in parallel to each other. Further, each molding cavity in each row is aligned with a corresponding molding cavity in the other row.
The lower mold member 20 has a central row of resin loading chambers 40 arranged at suitable spacing between the respective cavity rows C10, C20. Each loading chamber 40 receives a load of synthetic resin material such as a resin tablet 50, and a plunger 60 is slidably inserted in the loading chamber. Further, the resin loading chamber 40 communicates with a pair of runners 70, 80 which, in turn, communicate respectively with two molding cavities C10, C20 of the respective cavity rows through injection ports 70a, 80a.
In use of the mold 10 for multi-molding, a first leadframe R10 and a second leadframe R20 are arranged in parallel to each other between the respective mold members 20, 30. Thereafter, the respective resin tablets 50 are melted under heating, and the plungers 60 are pushed in deeper for supplying the fluidized resin into the molding cavities C10, C20 through the runners 70, 80 and the injection ports 70a, 80a. As a result, the electronic components E10, E20 carried on the leadframes are packaged in the resin.
Normally, the respective leadframe R10, R20 have specific orientation or directivity because the circuit arrangement on each electronic component E10, E20 is not symmetrical. Thus, the resin injection ports 70a, 80a for all of the molding cavities C10, C20 must be located at corresponding corner portions with respect to the electronic components E10, E20 in order to provide uniform quality for all of the products.
Further, the respective leadframes R10, R20, which are located on both sides of the row of resin loading chambers 40, must be arranged in opposite orientation. Specifically, as shown in FIG. 4, the first leadframe R10 is made to have its leading and trailing edges R10a, R10b located oppositely to those R20a, R20b of the second leadframe R20. It should be appreciated that the terms "leading edge" and "trailing edge" are used here only for the convenience of indicting the specific orientation of the leadframe in relative sense but not in absolute sense.
As a result, the respective runners 70, 80 must be inclined to a great degree relative to a line PL which is perpendicular to the longitudinal direction of the leadframes R10, R20. Thus, the runners become inevitably long, consequently necessitating the use of slow-hardening resin for packaging the electronic components E10, E20. For this reason, the productivity of the prior art method is relatively low, and the production cost increases.
Moreover, when each resin loading chamber 40 is commonly used for supplying resin to four molding cavities C10, C20, two kinds of runners 70', 70", 80', 80" must be provided which are different in length, as shown in FIG. 6. In this case, not only one kind of runners 70", 80' become unacceptably long, but also the difference in length between the runners results in uneven quality of the products.